The present invention relates to texturing of magnetic data storage media, and more particularly to the texturing of dedicated transducing head contact zones of such media to minimize system resonance.
Laser texturing of magnetic disks, particularly over areas designed for contact with data transducing heads, is known to reduce friction and improve wear characteristics as compared to mechanically textured disks. Traditional laser texturing involves focusing a laser beam onto a disk substrate surface at multiple locations, forming at each location a depression surrounded by a raised rim as disclosed in U.S. Pat. No. 5, 062,021 (Ranjan) and U.S. Pat. No. 5,108,781 (Ranjan). An alternative, as disclosed in International Publications No. WO 97/07931 and No. WO 97/43079, is to use a laser beam to form domes or nodules, rather than rims. In some cases, each of the domes is surrounded by a raised rim. The features can have either circular or elliptical profiles.
Collectively, the texturing features form a texture pattern or distribution throughout the head contact zone. A particularly preferred pattern is a spiral, formed by rotating the disk at a controlled angular speed while moving a laser radially with respect to the disk. The laser is pulsed to form the individual texturing features. For example, the disk can be rotated to provide a circumferential speed of about one meter per second. Then, operating the laser at 50,000 pulses per second provides a 20 micron circumferential pitch, i.e. distance between adjacent texturing features. The radial speed of the laser controls the radial pitch or spacing between adjacent turns of the spiral, which also can be about 20 microns.
Although this approach has been highly successful in terms of reducing dynamic friction and improving the wear characteristics of dedicated transducing head contact zones, the regular, repeating pattern of the laser texture features produces strong input excitations based on the fundamental frequency of the circumferential pitch, including higher order harmonics. When the excitation frequencies coincide with natural frequencies of the slider or its gimbal and support system, resonance occurs which results in a high amplitude acoustic energy signal, which can increase the difficulty of determining the glide avalanche breaking point (a disk/transducing head spacing value) and yield a false indication that the disk has failed a glide test.
In addition to their resonance effects, regularly spaced apart texturing features are thought to cause transducing head disturbances by intermittent contact of texturing-feature peaks with the data transducing head during disk accelerations and decelerations. Also, the texturing features contribute to turbulence in the air bearing that supports the transducing head slider during portions of accelerations and decelerations. At close non-contacting proximity of the head, pressure modulation of the air bearing can induce head resonance.
Several previously proposed media texturing alternatives address these difficulties to a degree. For example, the aforementioned International Publication Number WO 97/43079 includes the observation that mechanically textured disks, as compared to laser textured disks, produce less acoustic energy during head take-off and landing. A noise-reducing texturing alternative is discussed therein; namely, rows of rims connected to one another at their ends, as shown in FIG. 15 of the publication. In U.S. patent application Ser. No. 09/381,079 now U.S. Pat. No. 6,229,670, entitled xe2x80x9cLow Resonance Texturing of Magnetic Mediaxe2x80x9d, filed Mar. 13, 1998, resonance-reducing texturing is disclosed in the form of elongate circumferential ridges, most notably a continuous ridge in the shape of a spiral throughout the transducing head contact region. Although both of these alternatives afford considerable reduction in noise during head take-off and landing, there remains a need for noise-reducing texturing arrangements with substantial spacing between adjacent texturing features. These arrangements frequently are preferred to due to lower manufacturing costs and better potential for producing a uniform roughness throughout the head contact zone.
Therefore, it is an object of the present invention to provide an array of texturing features adapted to impart a desired surface roughness to the dedicated transducing head contact zone of a magnetic recording medium while minimizing undesirable resonant frequency effects.
Another object is to provide a magnetic data storage medium in which a head contact zone has a topography comprised of multiple texturing features in a pseudo-random array with irregular spacing intervals between adjacent texturing features, at least in a selected direction along the storage medium.
A further object is to provide a process for laser texturing a data storage medium by subjecting the storage medium to intermittent exposures according to a pseudo-random sequence of timing intervals between successive exposures, to cause an irregular spacing between adjacent texturizing features.
Yet another object is to provide magnetic data storage media that exhibit the highly favorable dynamic friction and wear characteristics of laser textured media, and further exhibit low resonance interactions with transducing heads and their support structure during head take-offs and landings.
To achieve these and other objects, there is provided a magnetic data storage medium. The medium includes a substrate body formed of a non-magnetizable material and a magnetizable film disposed over the substrate body. The recording medium has a substantially planar surface including a contact region adapted for a surface engagement with a magnetic data transducing head during accelerations and decelerations of the recording medium in a predetermined direction with respect to the transducing head. Multiple texturing features are formed in the contact region. The features protrude outwardly from a nominal surface plane of the substantially planar surface, and cooperate to define a surface roughness of the contact region. The texturing features are spaced apart from one another and arranged to define an irregular spacing between adjacent texturing features in the predetermined direction.
Preferably the texturing features are arranged to preserve a desired density (or permitted range of densities) as well as to provide irregular spacing. To this end, texturing features can be formed in a sequence in which actual intervals between adjacent features vary about a nominal spacing, and further vary about a range (maximum spacing less the minimum spacing) less than the nominal spacing. The nominal spacing can be selected with the desired feature density in mind. In the most preferred arrangement, spacing intervals occur randomly throughout the permitted range.
Typically the recording medium is a magnetic disk, with an annular contact region. Then, the predetermined direction is circumferential with respect to the disk, and the irregular interval is the circumferential pitch. A psuedo-random texture pattern throughout a head contact region can be formed as a single, spiral sequence of texturing features. The spiral provides essentially circumferential turns, with a selected, preferably constant radial pitch between adjacent turns.
The texturing features preferably are substantially uniform in their degree of extension away from the nominal plane, usually considered in terms of height above a horizontal nominal plane. This imparts a desired uniformity to the surface roughness throughout the contact region. The texturing features, when formed as laser nodules or bumps, are rounded and substantially free of sharp edges, and have heights in the range of about 5-30 nm.
Further in accordance with the invention, there is provided a process for surface texturing a magnetic data storage medium, including:
a. directing a coherent energy beam toward a magnetic storage medium; and
b. causing the coherent energy beam to impinge upon a selected surface of the storage medium at a plurality of different locations thereon, altering the topography of the selected surface at each location by forming a texturing feature, while selecting the locations to provide an irregular spacing between adjacent texturing features in at least one predetermined direction along the selected surface.
When the data storage medium is a magnetic disk, texturing involves disk rotation to provide a circumferential velocity, in concert with controlling the rate or frequency of laser exposures. One suitable approach involves rotating the disk to maintain a constant circumferential speed, while varying the timing of laser energy exposure episodes, either by controlling the laser itself or an optical component intermediate to the laser and the disk.
In one preferred texturing arrangement, a laser operated in the CW (continuous wave) mode provides a beam directed through an accousto-optic modulator, controlled by a pseudo-random pulse generator. The result is a pseudo-random sequence of texturing features that corresponds to the pseudo-random timing of the laser exposures. While other alternatives are conceivable, e.g., randomly varied disk rotation, considerably more precision is possible by varying the laser exposure timing rather than disk movement.
A pulse laser, randomly triggered, can be used in lieu of the CW laser and accoustal-optic modulator combination, although it is felt to afford less precision by comparison to the preferred combination.
Thus in accordance with the present invention, the transducing head contact zones of magnetic data storage media can be laser textured to form multiple spaced apart bumps or nodules that provide superior wear and friction characteristics, yet do not produce undesirable resonance effects during the take-offs and landings of transducing heads. A pseudo-random variance in spacing between adjacent texturing features, taken in the direction of medium/head relative movement, is particularly effective in reducing input excitations based on fundamental frequencies and their harmonics resulting in improved media performance.
For a further appreciation of the above and other features and advantages, reference is made to the following detailed description and to the drawings, in which:
FIG. 1 is a plan view of a magnetic data storage disk having a pseudo-random texture array in accordance with the present invention, and a data transducing head supported for generally radial movement relative to the disk;
FIG. 2 is an enlarged partial sectional view of the magnetic disk in FIG. 1;
FIG. 3 is a partial top plan view of a magnetic data storage disk with a texture pattern of discrete nodules according to the traditional laser texturing approach;
FIG. 4 is a schematic representation of a surface profile of the contact zone in FIG. 3, taken in a circumferential direction;
FIG. 5 is a graph showing excitation amplitude as a function of frequency, with respect to the disk of FIG. 3;
FIG. 6 is an enlarged partial top plan view of the data storage disk shown in FIGS. 1 and 2, showing the textured head contact zone;
FIG. 7 is a schematic representation of a surface profile of the head contact zone in FIG. 6, taken in a circumferential direction;
FIG. 8 is a chart showing excitation amplitude as a function of frequency, with respect to the head contact zone in FIG. 6;
FIG. 9 is a diagramatic view of a texturing system for forming the pseudo-random texture shown in FIG. 6;
FIG. 10 is a partial top plan view of an alternative data storage disk textured according to the present invention;
FIG. 11 is a sectional view of the disk in FIG. 10; and
FIG. 12 is a diagramatic view of an alternative embodiment texturing device.